Choose one of the following. (1) Summon X Forest Bat tokens. X equals the number of enemy cards on the field. (2) Give each Forest Bat token on your field +1/+1.
QIf there are no Forest Bats on my field, can I still play this spell with option 2?
AYes, you can.
QIf each player has 5 cards on their field, can I still play this spell with option 1?
AYes. Even if you can't summon any Forest Bats, you can still choose option 1 and play this spell.